Diesel powered over the road trucks usually travel long distances and must carry considerable amounts of fuel. A typical semi-tractor 10 is shown in FIG. 1. The semi-tractor has a pair of large fuel tanks 12 and 14 mounted in tandem on the sides of the truck.
In the typical prior art fuel system shown schematically in FIG. 2, fuel is drawn from a lower portion of a first fuel tank 12 through a fuel delivery line 16. Fuel delivery line 16 is connected to the remainder of the truck fuel system which is not shown. The typical fuel system may include such items as a fuel filter/water separator, fuel pump, fuel rail, and eventually the fuel injectors that deliver the fuel into the cylinders of the engine. Many diesel engines also have an overflow line 18, through which fuel which has been delivered to the fuel rail but which has not been consumed by the engine, is returned to the fuel tanks. Because the fuel has absorbed energy due to the action of the fuel pump, the returning fuel is typically much warmer than the fuel in the tanks.
The fuel level in tanks 12 and 14 is typically equalized by a bottom connecting line 20. Connecting line 20 extends below the bottom portions of the fuel tanks. It is desirable to keep the fuel in both tanks at the same level to maintain an equal weight distribution on the truck as well as to ensure all available fuel is used.
Connecting the fuel tanks through a bottom connecting line has disadvantages. First, because the line connects the tank bottoms and extends below the lower portions of the tanks, contaminants, such as water, can collect in the connecting line. If the water freezes, the connecting line may be blocked. Another potential problem is that if the connecting line is accidentally broken, all the fuel in both fuel tanks may be lost.
Another drawback associated with typical prior art fuel systems is that the fuel returning from the engine via overflow line 18 can become very warm during the summer months. This can increase the temperature in fuel tank 12. The fuel being delivered to the engine may get so hot that it will no longer burn efficiently. In addition, hot fuel may interfere with the operation of electronic fuel control systems which are common on many new trucks.
Another problem with conventional fuel systems is that diesel fuel naturally becomes thick and viscous in cold temperatures. When the truck is operated in winter conditions, wax crystals may form in the diesel fuel making it difficult to achieve fuel flow to the engine. Fuel heating devices are often employed during winter months to maintain fuel flow from the fuel tanks to the engine. These devices add to the cost of the truck.
Thus there exists a need for a fuel system for a diesel truck that avoids the problems associated with clogging of bottom connecting lines between the fuel tanks, loss of fuel due to line breakage, overheating of fuel in summer and the need to employ special fuel heating devices in winter.